Mesoporous compound comprising a mineral phase of aluminum and cerium, titanium or zirconium oxide particles and, optionally, an element in solid solution in said particles, the preparation method thereof and uses of same

ABSTRACT

The invention relates to an ordered mesoporous or mesostructured compound comprising a mineral phase of aluminium in which at least partially crystalline particles of a cerium, titanium or zirconium compound are dispersed. The inventive compound is characterised in that the chemical consistency thereof is such that the heterogeneity domains are at most 100 nm 2  The invention also relates to the aforementioned ordered mesoporous or mesostructured compound which comprises at least one element M in solid solution in said particles. Moreover, the invention relates to the methods of preparing said ordered mesoporous or mesostructured compounds. The inventive materials can be used, for example, in the field of catalysis.

A subject of the present invention is a homogeneous mesostructuredcompound comprising a mineral phase of alumina, and particles of cerium,titanium or zirconium oxide.

The invention also relates to said ordered mesoporous or mesostructuredcompound which comprises at least one element M in solid solution insaid particles.

The invention also relates to the processes for preparing said orderedmesoporous or mesostructured compounds.

In the strict sense of the term, what are called mesoporous compoundsare solids having, within their structure, pores possessing anintermediate size between that of micropores of zeolites-type materialsand that of macroscopic pores.

More precisely, the expression “mesoporous compounds” basicallydescribes a compound which specifically comprises pores with an averagediameter comprised between 2 and 50 nm, described by the term“mesopores”. Typically, these compounds are amorphous silicas-type orparacrystalline compounds in which the pores are generally distributedin random fashion, with a very wide pore-size distribution.

Regarding the description of such compounds, reference can in particularbe made to Science, vol. 220, pp. 365-371 (1983) or also to the Journalof Chemical Society, Faraday Transactions, 1, vol. 81, pp. 545-548(1985).

On the other hand, what are called “structured” compounds are for theirpart compounds having an organized structure, and characterized moreprecisely by the fact that they have at least one diffusion peak in aradiation-diffusion diagram of the X-ray or neutron-diffusion type. Suchdiffusion diagrams as well as the method for obtaining them are inparticular described in Small Angle X-Rays Scattering (Glatter andKratky—Academic Press London—1982).

The diffusion peak observed in this type of diagram can be associatedwith a repetition distance characteristic of the compound considered,which in the remainder of the present description will be called the“spatial repetition period” of the structured system.

On the basis of these definitions, by “mesostructured compound” is meanta structured compound possessing a spatial repetition period comprisedbetween 2 and 50 nm. The organized structure present in such a materialwill here be called the “mesostructure”.

Ordered mesoporous compounds for their part constitute a particular caseof mesostructured compounds. These are in fact mesoporous compoundswhich have an organized spatial arrangement of the mesopores present intheir structure, and which therefore effectively possess a spatialrepetition period associated with the appearance of a peak in adiffusion diagram.

Ordered mesoporous or mesostructured compounds comprising a mineralphase are well known and are very useful, in particular in the field ofcatalysis, absorption chemistry or membrane separation.

In particular ordered mesoporous or mesostructured compounds comprisinga mineral phase of alumina, within which at least partially crystallineparticles of a cerium, titanium or zirconium compound are dispersed, arevery useful in the field of catalysis. Also, in order to best adapt themto these different applications, attempts have been made to modify themin so as to improve their effectiveness in these different fields.

Ordered mesoporous or mesostructured compounds comprising a mineralphase of alumina within which mineral particles are dispersed are not infact perfectly chemically homogeneous, and consequently do not fullymeet industrial requirements.

An object of the invention is also to propose ordered mesoporous ormesostructured compounds comprising a mineral phase of alumina, withinwhich mineral particles are dispersed, said mesostructured compoundhaving a good chemical homogeneity and optionally comprising at leastone element M in solid solution in said particles.

To this end the present invention proposes according to a first variantan ordered mesoporous or mesostructured compound comprising a mineralphase of alumina, within which at least partially crystalline particlesof a cerium, titanium or zirconium compound are dispersed, characterizedin that it has a chemical homogeneity such that the heterogeneitydomains are at most 100 nm².

The invention also proposes a process for preparing said compound.

The advantage of the compounds according to the present invention isthat in addition to their great homogeneity these compounds arethermally stable up to temperatures of approximately 600° C. and even upto temperatures above 700° C. This stability is measured by comparisonswith the surface of a compound previously calcined at 500° C. By this ismeant that when the compound is subjected to a heat treatment for 6hours at the above-mentioned temperatures, in addition to thepreservation of the mesostructured character, a relatively goodmaintenance of the specific surface area is observed, that is to saythat, following the heat treatment, the specific BET surface area ofsaid compound does not generally vary by a factor exceeding 60%, thisfactor preferably remaining below or equal to 50%, and advantageouslybelow or equal to 40%. The variation factor of the BET surface areareferred to is calculated by the ratio (Si-Sf)/(Si), where “Si”describes the specific BET surface area measured after heat treatment at500° C.; and where “Sf” describes the specific BET surface area measuredafter heat treatment at 600° C. or 700° C.

Moreover, a need also exists for materials with further improvedproperties, for example for materials having an improved reducibility.

Attempts have been made to obtain what are called “doped” materials ofthis type, that is to say comprising a metal element in the oxideparticle, other than the metal element forming said particle, in solidsolution within the crystalline network of said particle. In fact,although it is currently known how to synthesize metal oxide particlesof very small dimensions (in particular of the cerium oxide, titaniumoxide, zirconium oxide type, of dimensions smaller than 10 nm), on theother hand it is known neither how to dope such particles byincorporating in them metal elements in solid solution, or directlysynthesize doped oxides in the form of particles with sufficiently smalldimensions and/or with a suitable surface area in order that their usein a texturing process results in the obtaining of a thermally stablemesostructure in a phase of alumina.

A second object of the present invention is the obtaining of such whatare called “doped” materials that meet these needs.

To this end the present invention proposes according to a second variantan ordered mesoporous or mesostructured compound comprising a mineralphase of alumina, within which at least partially crystalline particlesof a cerium, titanium or zirconium compound are dispersed, said compoundhaving a chemical homogeneity such that the heterogeneity domains are atmost 100 nm², characterized in that the particles comprise at least oneelement M in solid solution in said particles.

The invention also proposes a process for preparing said doped compound.

It was thus demonstrated that, unexpectedly, the integration of dopingmetal cations in solid solution in particles of a mesostructuredmaterial can be carried out at a relatively low temperature.

Moreover, the doped materials of the invention advantageously have astabilized specific surface area, high oxygen storage capacity (OSC) andimproved reducibility.

In addition, the advantage of the compounds according to this secondvariant of the invention is that in addition to their great homogeneity,these compounds are thermally stable up to temperatures of approximately600° C. and even up to temperatures above 650° C.

This stability is measured as indicated above by comparisons with thesurface area of a compound previously calcined at 500° C.

Other advantages and characteristics of the present invention willbecome clear on reading the following description and examples givenpurely by way of illustration and non-limitatively.

By specific surface area is meant, for the whole of the description, thespecific BET surface area determined by nitrogen adsorption according tothe ASTM standard D 3663-78 established on the basis of theBRUNAUER-EMMETT-TELLER method described in the periodical “The Journalof the American Chemical Society, 60, 309 (1938)”.

Firstly, according to a first variant, a subject of the invention is anordered mesoporous or mesostructured compound comprising a mineral phaseof alumina, within which at least partially crystalline particles of acerium, titanium or zirconium compound are dispersed, characterized inthat it has a chemical homogeneity such that the heterogeneity domainsare at most 100 nm².

As regards the mineral phase or matrix of alumina, by alumina is meantaluminium hydroxides Al(OH)₃, aluminium oxyhydroxides AlO(OH) oraluminium oxides Al₂0₃. At least partially crystalline particles of acerium, titanium or zirconium compound are dispersed within this mineralphase. These cerium, titanium, zirconium particles are particles ofnanometric dimension.

It will be noted here that the mineral phase or matrix does not embraceall of the particles of nanometric dimension that it contains. In thiscase, the mineral phase acts as a binder between the particles, at leastpart of the surface area of which is thus accessible and released fromthe mineral phase. Thus, at least some of the particles are in contactwith the porous parts constituting the internal space, accessible by agas phase in particular, of the material. Therefore, in the remainder ofthe description, the term “binding phase” will sometimes be used inrelation to the mineral phase.

By “particles of nanometric dimension” is meant, within the meaning ofthe present invention, particles preferably of spherical or isotropicmorphology, at least 50% of the population of which possesses an averagediameter comprised between 1 and 10 nm and preferably at most 6 nm, witha preferably monodisperse granulometric distribution of these particles.Here and for the remainder of the description, the sizes of theparticles are measured by transmission electron microscopy (TEM).

In particular, the term “particles of nanometric dimension” can alsodescribe according to the invention strongly anisotropic rod-typeparticles, provided that, for at least 50% of the population of theseparticles, the average transverse diameter is comprised between 1 and 10nm and the length does not exceed 100 nm, with a preferably monodispersegranulometric distribution of these particles.

Preferably, the particles dispersed within the alumina matrix areparticles with a diameter of the order of 3 to 5 nm. The cerium,titanium or zirconium compounds of the particles are chiefly oxides.

It will also be noted that the binding mineral phase can itself also beconstituted by a collection of particles of nanometric dimension. Inthis case, the particles of alumina preferably have a diameter smallerthan that of the particles of the cerium, titanium or zirconiumcompounds, for example from 1 to 5 nm.

Therefore, as regards the structure of the compound of the invention,the latter has mineral walls which can be described as constituted bydiscrete domains of binding phase and particles of nanometric dimension.Advantageously, the mineral walls can be constituted by domains ofbinding phase possessing a smaller thickness compared with the thicknessof the domains of the particles of nanometric dimension.

These mineral walls delimit a pore volume with accessibility of thesurface areas of the particles of nanometric dimension of the cerium,zirconium or titanium compound by a gas phase or a liquid phase.

The particles of nanometric dimensions based on the compounds of theelements cerium, titanium or zirconium which are present in the materialof the invention are at least partially crystalline particles, withinwhich the metal oxide generally has a degree of crystallinity preferablyranging from 30 to 100% by volume. The degree of crystallinity by volumeof a given metal oxide, present within the particles of nanometricdimensions of the material of the invention, can be calculated by theratio of the area of the diffraction peak measured by X-ray diffractionfor a sample of the compound according to the invention to the area ofthe same diffraction peak measured for a control sample of said oxide inthe totally crystallized state, adjusted for the absorption coefficientsof the corresponding oxides.

The presence of these partially crystallized particles within themineral phase confers upon the mesostructured compounds or materials ofthe invention, in addition to an ordered arrangement of their network ofpores, an overall degree of crystallinity generally at least equal to10% by volume, and preferably at least 30% by volume, this overalldegree of crystallinity by volume being calculated by multiplying thedegree of crystallinity by volume determined experimentally for theparticles, according to the method described above, by the fraction byvolume of the material which is occupied by said particles. Moreparticularly still, the compound according to the present invention hasan overall degree of crystallinity by volume of at least 50% and stillmore preferably of at least 60%.

By “degree of crystallinity of a mesostructured material” within themeaning of the invention is meant the degree of crystallinity specificto the walls of the structure, which overall takes into account both anycrystallinity of the mineral phase of alumina or binding phase and thecrystallinity of the particles of nanometric dimensions included in thisbinding phase. In this connection, it must therefore be stressed thatthe crystallinity of the material, within the meaning of the invention,corresponds to a microscopic organization detectable in particular bydiffraction (for example by wide-angle X-ray diffraction), which is tobe distinguished in particular from the order presented, at a moremacroscopic level, by the mesostructure of the material.

The mineral phase of the mesostructured material of the presentinvention integrating the particles of nanometric dimension definedpreviously for its part constitutes a mineral phase, amorphous topartially crystalline, constituted by alumina.

More particularly said compound has a chemical homogeneity such that theheterogeneity domains are at most 25 nm².

By chemical homogeneity such that the heterogeneity domains are at mostx nm² is meant a compound which has a chemical homogeneity over asurface area of at least x nm². For example by chemical homogeneity suchthat the heterogeneity domains are at most 100 nm² is meant a compoundwhich has a chemical homogeneity over a surface area of at least 10nm×10 nm on ultramicrotomic sections. This means that there is nodifference in the chemical composition of the products of the inventionbetween different surface areas of 100 nm².

These homogeneity characteristics are determined by TEM-EDS analysis.More particularly, the heterogeneity domain was measured by theenergy-dispersion-spectroscopy (EDS) cartography method using atransmission electron microscopy (TEM) microprobe on ultramicrotomicsections. These analyses were carried out with a microscope equippedwith a 300 KV source (to be confirmed) and the ultramicrotomic sectionspossess a thickness of 80 nm, plus or minus 20 nm.

According to a second variant of the invention, the material of theinvention can contain a doping element. This element can be an element Maccording to a first embodiment, and/or M′ according to a secondembodiment. The element M is in solid solution in the particleconstituting the material, i.e. in the cerium, zirconium and/or titaniumoxide. This element M is in the cationic state, generally in solidinsertion and/or substitution solution, within the crystalline structureof the particle.

By element in solid solution within the particle is meant the presenceof this element as cation, in the capacity of insertion and/orsubstitution cation, within the crystalline oxide of the particlecharacteristically playing the role of a host crystalline network, saidcation of the element M generally representing strictly less than 50mol-% of the total quantity of metal cations present in the oxide, i.e.the cation integrated in solid solution is preferably a minority cationrelative to the cations constituting the metal oxide where it isintegrated in solid solution, the level of this cation in the element Mhowever being able to reach 50% in certain cases. A crystalline oxideintegrating cations in solid solution preserves the structure of thecrystalline oxide in the pure state, slight modifications to theparameters of meshes being observable however, for example in accordancewith Vegard's Law. A crystalline oxide integrating cations in solidsolution therefore generally has an X-ray-diffraction diagram similar tothat of the pure mixed oxide, with a greater or lesser peaks shift.

Generally, the element M is chosen from the rare earths and transitionmetals, capable of being integrated in cationic form in solid solutionwithin said particle. However, the metal M can be chosen morespecifically depending on the nature of the metal oxide of the particlewithin which it is integrated in solid solution. It will be noted thatthe quantity of metal M that can be introduced in solid solution withinthe oxide depends on the nature of said metal M and on the nature of theelement constituting said oxide.

Thus, when the particle is constituted by cerium oxide, the element Mpresent in solid solution can, generally, be chosen from the rare earthsother than cerium. In this case, the metal M can be more particularlylanthanum, yttrium, neodymium, praseodymium, dysprosium or europium. Theelement M can also be chosen from the transition metals capable of beingintegrated in cationic form in solid solution within an oxide of cerium,in particular zirconium, manganese and titanium. When the doping metal Mrepresents zirconium or a rare earth other than cerium, the quantity ofcations of the metal M that can be integrated in solid solution canrepresent a value such that the molar ratio M/Ce is at most 1. When thedoping metal M represents titanium, the quantity of titanium that can beintegrated in solid solution can represent a value such that the molarratio Ti/Ce is at most 0.5.

When the particle is constituted by zirconium oxide, the metal M presentin solid solution can be chosen from cerium and rare earths other thancerium. In this case, M can advantageously be cerium, lanthanum,yttrium, neodymium, praseodymium, dysprosium or europium. M can also bechosen from transition metals capable of being integrated in cationicform in solid solution within a zirconium oxide. When the doping metal Mrepresents cerium or another rare earth, the quantity of cations of themetal M that can be integrated in solid solution can represent a valuesuch that the molar ratio M/Zr is at most 1.

When the particle is constituted by titanium oxide, the metal M presentin cationic state in solid solution can also be chosen from rare earths,transition metals capable of being integrated in solid solution within atitanium oxide. The metal M can be more particularly manganese, tin,vanadium, niobium, molybdenum or antimony.

Finally, according to a particular embodiment, the element M is chosenfrom cerium, titanium, zirconium, manganese, lanthanum, praseodymium andneodymium, said element M being different from the element constitutingthe oxide of the particle (cerium, zirconium or titanium oxide).

According to a second more particular embodiment of the second variantof the invention, the compound is characterized in that said particlesof the compound include at least one element M′ at least in part ontheir surface.

This element M′ can be manganese, or an alkali or alkaline earth metal.

This element M′ can be in the form of metal cations and/or clustersbased on the metal M′ or on an alkali or alkaline earth metal and/orcrystallites of these same elements, these cations or clusters orcrystallites being dispersed, preferably homogeneously, at least in partin the surface of the oxide particle constituting the material, or eventhe whole surface.

By alkali is meant an element of Group IA of the periodic table.

The periodic table of the elements referred to here and in the remainderof the description is that published in the Supplement to the Bulletinof the Société Chimique de France no. 1 (January 1966).

Of the alkalis, sodium or potassium can more particularly be mentioned.

By alkaline earth is meant an element of Group IIA of the periodictable. This can in this case more particularly be barium.

Finally, the element M′ can be manganese.

Of course, this particular embodiment of the second variant of theinvention covers materials comprising several elements M′ in combinationchosen in particular from within the same group or between differentgroups. More particularly, manganese can be present combined with analkali or an alkaline earth element and still more particularly, themanganese can be combined with potassium.

According to this particular embodiment of the invention, the element M′is present in the material in the form of a salt. In this case, the saltcan in particular be a chloride, a sulphate or a carbonate.

According to another particular embodiment, the element M′ is present inthe material in the form of a hydroxide or an oxide or also anoxyhydroxide.

However, the element M′ can also be present at once in the same materialin the form of a salt, a hydroxide, an oxide or an oxyhydroxide.

The element M′ can finally be present in amorphous form or incrystallized form.

The crystallites can be for example crystallites of TiO₂ in anataseform, crystallites of ZrO₂.

The crystallites based on metal M′ described above generally have anaverage size smaller than or equal to 500 nm, preferably smaller than orequal to 200 nm. In general, these crystallites have an average size atleast equal to 2 nm.

By “cluster” based on the metal M′ is meant a polyatomic entity lessthan 2 nm in dimension, preferably less than 1 nm, comprising at leastatoms of the metal M′, in state of oxidation 0 or a higher state ofoxidation (typically, these are clusters based on oxide and/or hydroxidespecies of the metal M′, for example polyatomic entities within whichseveral atoms of the metal M′ are interconnected by —O— or —OH— bridges,each of the atoms of the metal M′ being able to be linked to one or more—OH groups). This variant can be used in particular in the case wherethe metal M′ is zirconium, manganese, or also a rare earth (inparticular lanthanum, yttrium, neodymium, praseodymium, dysprosium oreuropium).

According to a particular variant in the case where manganese iscombined with an alkali or an alkaline earth element, these elements canbe present in the material of the invention in a chemically bonded form.By this is meant that there are chemical bonds between the manganese andthe other element resulting from a reaction between them, these twoelements not being simply juxtaposed as in a simple mixture. Thus, theelements manganese and the other element can be present in the form of acompound or a mixed-oxide-type phase. This compound or this phase can inparticular be represented by the formula A_(x)MnyO₂₊δ (1) in which Adescribes the other element (alkali or alkaline earth) and 0.5≦y/x≦6.There can be mentioned as examples of the phase or compound of formula(1) those of vernadite, hollandite, romanechite or psilomelane,bimessite, todorokite, buserite or lithiophorite type. The compound canoptionally be hydrated. The compound can moreover have a Cdl₂-typelamellar structure. Formula (1) is given here by way of illustration,but it would not go beyond the scope of the present invention if thecompound had a different formula, provided of course that the manganeseand the other element were chemically well bonded.

When the cations, clusters and/or crystallites of an alkali or alkalineearth metal are dispersed on the surface of the oxide constituting thematerial as has just been described, the quantity of this metal in thisform, expressed in moles relative to the moles of the constitutive oxideor oxides and of metal M′, is generally comprised between 2% and 30%,preferably between 4% and 25%.

The characteristics of the compound according to the invention, moreparticularly the homogeneity, described in the first variant of theinvention are also valid for compound according to the second variant.

In a preferred embodiment, the compound according to the invention cancomprise a mineral phase of alumina within which particles of cerium,doped or not, are dispersed. In this case the alumina and cerium arepresent in a quantity such that the atomic ratio Ar=Al/(Ce+Al) is atmost 50%, preferably at most 25%.

The compound according to the invention, doped or not, advantageouslypossesses a mesostructured structure the overall thickness of the wallsof the compound of which is comprised between 2 and 10 nm.

The compound according to the invention, doped or not, advantageouslypossesses a mesoporous structure comprising pores with a size comprisedbetween 2 and 12 nm, preferably between 3 and 9 nm.

The compound, doped or not, according to the invention is advantageouslya solid which has at least locally one or more mesostructure(s) chosenfrom:

-   -   mesoporous mesostructures of P63/mmc three-dimensional hexagonal        symmetry, P6mm two-dimensional hexagonal symmetry, Ia3d, Im3m or        Pn3m three-dimensional cubic symmetry; or    -   vesicular or lamellar-type mesostructures,    -   vermicular-type mesostructures.

Regarding the definition of these different symmetries and structures,reference can be made for example to Chemical Materials, vol. 9, No. 12,pp. 2685-2686 (1997) or also to Nature, vol. 398, pp. 223-226 (1999) oralso to Science Vol. 269, pp 1242-1244 (1995).

On the other hand, the compounds according to the first variant of theinvention have a good temperature stability and a high specific surfacearea, greater than 650 m²/cm³ for a calcination temperature of 500° C.over 6 hours. This specific surface area expressed in m²/cm³ is obtainedby multiplying the surface area generally measured in m²/g by thedensity of the composite material. For a compound the particles ofnanometric dimension of which are based on a cerium compound, thisspecific surface area is preferably comprised between 100 and 500 m²/g.

On the other hand, the compounds according to the second variant of theinvention have a good temperature stability and a high specific surfacearea, advantageously greater than 650 m²/cm³, preferably greater than900 m²/cm³, and still more preferably greater than 1200 m²/cm³ for acalcination temperature of 400° C. over 6 hours. This specific surfacearea expressed in m²/cm³ is obtained by multiplying the surfacegenerally measured in m²/g by the density of the composite material. Fora compound the particles of nanometric dimension of which are based on acerium compound, this specific surface area is preferably comprisedbetween 100 and 300 m²/g.

In the particular case of a doped material constituted by a bindingphase of alumina and cerium oxide particles and in which M is titanium,this surface area can be at least 100 m₂/g, more particularly at least125 m²/g and still more particularly at least 150 m²/g.

The pore volume of the doped materials of the invention is generally atleast 0.10 cm³/g, more particularly at least 0.15cm³/g and still moreparticularly at least 0.20 cm³/g.

One of the advantages of the materials according to the second variantof the invention based on cerium oxide particles is their reducibility.This “reducibility” of a material according to the invention can bedemonstrated by treating the material with hydrogen and by analyzing therate of conversion of the cerium in oxidation state IV initially presentinto cerium in oxidation state III in the material obtained after thetreatment, according to the overall reaction below:2CeO₂+H₂→Co₂03+H20

The reducible character of a doped material according to the inventioncan thus in particular be quantified by the rate of conversion measuredat the end of what is called a “TPR” protocol, described below:

-   -   in an Altamira AMI-1-type apparatus equipped with a silica        reactor, a sample of 100 mg of the solid to be tested is placed        at ambient temperature (generally between 15° C. and 25° C.)        under a gaseous flow of a hydrogen/argon mixture with 10%        hydrogen by volume, at a flow rate of 30 mL per minute.    -   the temperature is increased to 900° C. at a constant        temperature rise gradient of 10° C. per minute. Using a 70 mA        thermal conductivity detector, the quantity of hydrogen        collected by the material from the surface lacking the hydrogen        signal from the base line at ambient temperature to the base        line at 900° C. is determined.

At the end of such a test, a rate of conversion of the cerium IV speciesinitially present is generally measured which is at least 30%, thisconversion rate being advantageously at least 40%, more preferably atleast equal to 50%.

It is to be noted moreover that the reduction peak of the ceriumdetermined by the above protocol is centred on temperatures of at most450° C., preferably at most 400° C. and still more preferably at most375° C.

The process according to the invention will now be described.

The process for preparing the product according to the first variant ofthe invention comprises the following stages:

-   -   1) an aqueous mixture is formed comprising:        -   a colloidal dispersion of alumina        -   at least one texturing agent        -   a colloidal dispersion of a cerium, titanium or zirconium            compound in which the cerium, titanium or zirconium compound            is functionalized by a surfactant of formula X-A-Y in which:            -   a) X is a function that complexes the cation of the                cerium, titanium or zirconium compound of the colloidal                dispersion;            -   b) A is a linear or branched alkyl-type group;            -   c) Y is an amine or hydroxy group;

the colloidal dispersions of alumina and of the cerium, titanium orzirconium compound having a conductivity below 25 mS/cm;

-   -   2) the water is eliminated from the above-mentioned mixture;    -   3) the texturing agent is eliminated.

The process for preparing the product according to the second variant ofthe invention comprises the stages 1) to 3) previously described andalso comprises, after the above-mentioned stage 3), the followingstages:

-   -   4)-(a) the material obtained previously is brought into contact        with a solution of the element M which has a concentration of        this element of at most 2 mol/l;        -   (b) the material obtained after this bringing into contact            with said solution is calcined at a temperature of at most            500° C.;        -   (c) if appropriate stages (a) and (b) are repeated until a            material having the desired level of element M is obtained.

Advantageously the colloidal dispersions used to prepare the mixture ofstage 1 are of the type of those described in particular in the patentsEP 206 906 and EP 208 580 (in particular for the colloidal dispersion ofcerium), or in Materials Letters 40 (1999) 52-58 (in particular for thecolloidal dispersion of alumina). These dispersions can also be obtainedin particular by acid treatment and washing of dispersions of ultrafinepowders obtained for example by high-temperature synthesis processes ofthe type of combustions of metal chlorides in a flame, known to a personskilled in the art.

Preferably, the concentration of particles in the dispersions usedaccording to the invention expressed in cation moles is greater than 1M.

The colloidal dispersion of alumina preferably has a pH comprisedbetween 3 and 6. Moreover it is preferable to use a colloidal dispersionof alumina the size of the particles or colloids of which is comprisedbetween 1 nm and 5 nm.

The colloidal dispersion of a cerium, titanium or zirconium compoundpreferably possesses particles or colloids the average size of which iscomprised between 3 nm and 8 nm.

The colloidal dispersions of alumina and of cerium, titanium orzirconium compound used are purified by washing by the ultrafiltrationtechnique in order to have the above-mentioned level of conductivity.The conductivity value given above is for a measurement carried out ondispersions with a pH comprised between 2 and 5 and with a cationconcentration of 1 M. This conductivity measured under these conditionsis thus below 25 mS/cm, advantageously below 8 mS/cm.

The initial medium formed during stage (1) is an aqueous medium, but itcan also be a hydro-alcoholic medium, and preferably in this case awater/ethanol medium.

The mixture prepared at the end of stage I comprises at least onetexturing agent.

This texturing agent present in the mixture is a surfactant-typeamphiphilic compound, in particular a copolymer. The essentialcharacteristic of this compound is that it is capable of forming liquidcrystal phases in the reaction mixture, so as to lead to the formationof a mineral matrix possessing an organized mesostructure byimplementing the “LCT” (Liquid Crystal Templating) texturing mechanism.

However, in order to implement a neutral texturing process which has theadvantage of leading to an increase in the thickness of the wallsobtained and therefore to an improvement in the stability of the finalstructure, the texturing agent used in the process according to theinvention is preferably a compound that is not charged under theconditions of implementation of the process.

Advantageously, the texturing agent according to the invention is anon-ionic copolymer-type surfactant, and in particular chosen fromdiblock or triblock-type block copolymers.

Preferably, in the case of a process carried out in aqueous orhydro-alcoholic media, a non-ionic block copolymer-type texturing agentis used, and more preferably a poly(ethylene oxide)-poly(propyleneoxide)-poly(ethylene oxide) triblock copolymer known as PEO-PPO-PEO(also called (EO)_(x)-(PO)_(y)-(EO)_(z)) of the type of those describedin particular by Zhao et al. in the Journal of the American ChemicalSociety, vol. 120, pp. 6024-6036 (1998), and marketed by BASF under thegeneric tradename of Pluronic®. Advantageously non-ionic surfactants canalso be used, such as the grafted poly(ethylene oxides) (EO)_(x)C_(y)marketed by Aldrich under the tradenames Brij® or Tween®; or alsonon-ionic surfactants of the sorbitan-type of those marketed by Flukaunder the tradename Span®.

The texturing agent can also be a poly(ethylene oxide)-poly(isopropene)block copolymer or a poly(ethylene oxide)-poly(isoprene) blockcopolymer.

According to the invention the colloidal dispersion of the cerium,titanium or zirconium compound is characterized in that the cerium,titanium or zirconium compound is functionalized by a surfactant offormula X-A-Y. The surfactant can also be found in free form within thedispersion.

This surfactant is an organic compound in which A is a linear orbranched alkyl group, optionally substituted, which can for examplecomprise from 1 to 12 carbon atoms, preferably between 2 and 8 carbonatoms.

The function X is a function that complexes the metal cation of thecolloid of the colloidal dispersion of the cerium, titanium or zirconiumcompound. By complexing function is meant a function which allows theformation of a complexing bond between the cation of the colloid, forexample the cerium cation, and the surfactant. This function can be afunction of the phosphonate —PO₃ ²⁻, or phosphate-PO₄ ²⁻,carboxylate-C0₂ ⁻, or sulphate-So₄ ²⁻, sulphonate-SO₃ ² type forexample.

The function Y is an amine or hydroxy function. It can be an aminefunction of —NH₂, —NHR₂, or —NR₃R₂, or —NH₄ ⁻, R₂ and R₃ type, identicalor different, describing a hydrogen or an alkyl group comprising from 1to 8 carbon atoms. It can also be an OH function. Among the agents withOH functions, there can for example be mentioned glycolic acid, gluconicacid, lactic acid, hydroxybenzoic acid, glycerol phosphate disodium.

Among the surfactants which are particularly suitable for the inventionthere can be mentioned the amino acids, and in particular the aliphaticamino acids. In particular there can be mentioned the amino acidsconstituting proteins with the structure R—CH(NH₂)—COOH where R is analiphatic radical. By way of example there can be mentioned leucine,alanine, valine, isoleucine, glycine and lysine.

The preferred surfactant according to the invention is aminohexanoicacid.

Advantageously the quantity of surfactant used to functionalize thecompound of this dispersion is expressed by the Rb ratio, determined bythe following formula:${Rb} = \frac{{Number}\quad{of}\quad{moles}\quad{of}\quad{function}\quad X}{\begin{matrix}{{{Number}\quad{of}\quad{moles}\quad{of}\quad{cerium}},} \\{{titanium}\quad{or}\quad{zirconium}\quad{oxide}}\end{matrix}}$

The Rb ratio is advantageously comprised between 0.1 and 0.5.

Preferably, the functionalization of the cerium, titanium or zirconiumcompound is carried out by bringing a dispersion of said compound intocontact with the surfactant.

According to a preferred variant of the invention, the startingcolloidal dispersion of alumina can also be a dispersion in which thecolloids of alumina can be functionalized by a surfactant of the X-A-Ytype, identical to or different from the surfactant of the colloidaldispersion of the cerium, zirconium or titanium compound.

Preferably, an elimination of any free surfactant molecules is carriedout by ultrafiltration washing.

The formation of the mixture of stage 1) of the process according to theinvention is carried out by simply bringing into contact theconstituents of the mixture, namely the dispersion of alumina, thetexturing agent and the colloidal dispersion functionalized according tothe method described above. This simple bringing into contact takesplace in aqueous or hydroalcoholic media.

The conditions for implementing stage 1) are such that they make itpossible to obtain at the end of stage 1) a mixture which possesses aconductivity (measured at a cation concentration of 1M) which isadvantageously at most 25 mS/cm. Preferably the conductivity of themixture (measured under the same conditions) will be at most 8 mS/cm.

In order to obtain such a conductivity, colloidal dispersions havingthis conductivity will be chosen.

The colloidal dispersions and the texturing agent are used in quantitiessuch that the ratio:$\phi = \frac{{volume}\quad{of}\quad{the}\quad{colloids}}{{{volume}\quad{of}\quad{the}\quad{colloids}} + {{volume}\quad{of}\quad{the}\quad{texturing}\quad{agent}}}$is preferably comprised between 0.1 and 0.6, and more particularlybetween 0.1 and 0.4.

By volume of the colloids is meant the value obtained by dividing themass of the colloids present in the dispersion or dispersions by thetheoretical density of the colloid or colloids, and by volume of thetexturing agent is meant the value obtained by dividing the mass of thetexturing agent by the theoretical density of the latter.

The second stage of the process consists of at least partiallyeliminating the water from the starting mixture. This stage can becarried out by evaporation in the open air or under a fume hood, andpreferably at ambient temperature. The evaporation can advantageously becarried out in a thin layer, with a thickness of less than 5 mm.High-temperature freeze-drying can also be carried out.

The third stage of the process for preparing the compound of theinvention consists of eliminating the texturing agent.

This stage can be in particular be carried out by a heat treatment. Inthis case, the heat treatment is advantageously carried out inaccordance with a temperature rise profile comprised between 0.2° C. perminute and 3° C. per minute, and preferably following a temperature riseprofile comprised between 0.5° C. per minute and 2° C. per minute, so asnot to degrade the material. This temperature increase is generallycarried out up to a temperature allowing the elimination of thetexturing agent, preferably up to a temperature comprised between 300°C. and 600° C.

On the other hand, the elimination of the texturing agent can also becarried out by entrainment by a solvent. It is to be noted that theentrainment by a solvent is facilitated by the fact that a non-chargedamphiphilic compound is preferably utilised, which induces a texturingagent-matrix interaction weak enough to allow this type of elimination.

Advantageously, the solid obtained at the end of stage 3 can moreover besubjected to an additional heat treatment, and in particular to acalcination. The aim of this optional additional heat treatment is toincrease the crystallinity of the material obtained, and eliminateimpurities such as nitrate anions and surfactants.

The fourth stage of the process consists of bringing the materialobtained in the preceding stages of the process into contact with asolution of the element M.

The solution of the element M used in the case of the process accordingto the invention is usually an aqueous solution based on salts of thiselement. The salts of inorganic acids such as nitrates, sulphates orchlorides can be chosen. The salts of organic acids and in particularthe salts of saturated aliphatic carboxylic acids or the salts ofhydroxycarboxylic acids can also be chosen. By way of examples, therecan be mentioned formates, acetates, propionates, oxalates or citrates.It is however possible to use an aqueous or hydro-alcoholic solutioncomprising cations. of the metal M in the complexed state, or also asolution, generally in anhydrous organic solvent medium, comprising analkoxide of the metal M.

When the element M is titanium, a titanium alkoxide in acidifiedhydroalcoholic medium can more particularly be used.

The solution which is brought into contact with the material has aconcentration of this element M which is at most 2M, preferably at most1.2M. A higher concentration risks preventing the formation of a solidsolution of the element M in the oxide constituting the particle.

The bringing into contact can be done by immersing the startingmesostructured material within a solution comprising the element M thensubjecting the medium obtained to a centrifugation. Generally, thecentrifugation is carried out at 2000 to 5000 rpm, for a periodgenerally not exceeding 30 minutes.

According to a particular embodiment, the bringing into contact of theelement M with the cerium, titanium or zirconium compound is done by dryimpregnation. The dry impregnation consists of adding to the product tobe impregnated a volume of an aqueous solution of the element M which isequal to the pore volume of the material to be impregnated.

The solid obtained at the end of phase (a) of the fourth stage of theprocess is then subjected to a calcination. This calcination stage(phase (b) of the fourth stage) is essentially intended to realize an atleast partial integration of cations of the element M in solid solutionwithin the oxide constituting the particle. To this end, thiscalcination takes place at a temperature at least equal to 300° C., thistemperature being preferably at least equal to 350° C. but it ispreferably at most 400° C. and advantageously at most 500° C. Highertemperatures are not required for the integration of the cations of theelement M within the oxide of the particle. In this connection, it mustbe stressed that the process of the present invention surprisingly makesit possible to integrate metal cations in solid insertion and/orsubstitution solution within the metal oxide of the particle at lowtemperatures, which in particular makes it possible to obtainmesostructured materials having very large specific surface areas. Inparticularly advantageous fashion, the calcination stage can be carriedout by subjecting the solid to a temperature gradient, from an initialtemperature comprised between 15 and 95° C., to a final temperaturecomprised between 350° C. and 1000° C., advantageously with atemperature rise comprised between 0.5° C. per minute and 2° C. perminute, and with one or more intermediate temperature holding stages,preferably comprised between 350 and 600° C., for variable periods,generally comprised between 1 hour and 24 hours. Optionally, thepreparation process of the invention can comprise a drying stage, priorto the calcination stage 4) (b). In this case, this prior drying isgenerally carried out as slowly as possible, in particular so as topromote ion exchanges. To this end, the drying is most often carried outat a temperature comprised between 15 and 80° C., preferably at atemperature below 50° C., or even below 40° C., and advantageously atambient temperature. This drying can be carried out under an inertatmosphere (nitrogen, argon) or under an oxidizing atmosphere (air,oxygen) depending on the compounds present in the material. In the casewhere the metal M is introduced into the material in the form of analkoxide, the drying is advantageously carried out under a water-freeatmosphere.

According to a particularly advantageous embodiment, the process of theinvention can comprise, following stages 4) (a) and 4) (b), one or moresubsequent cycles of bringing into contact/calcination implementingstages of type 4) (a) and 4) (b), carried out on the solid obtained atthe end of the preceding cycle. By implementing this type of processwith several successive cycles of bringing into contact/calcination, avery good incorporation of the element M in solid solution within theparticles of oxides is achieved. These cycles are repeated until amaterial having the desired level of element M is obtained. It is alsopossible to envisage the implementation of several cycles of bringinginto contact/calcination using separate M-type doping elements, wherebyit is possible to obtain materials constituted by oxides doped withseveral metal elements in solid solution.

To prepare materials according to the variant described above in whichcations, clusters and/or crystallites of the metal M′ or of an alkali oralkaline earth metal are dispersed on the surface of the oxideconstituting the material, solutions of this element (M′ or alkalis oralkaline earths) are used at high concentrations, for example at least1.5M and/or the stage of bringing into contact with this solution isrepeated after saturation of the oxide constituting the material in theform of solid solution with this element . The process for preparingthese materials, containing M′, is the same as that described for thepreparation of the materials containing the element M and comprises thestages 1, 2, 3 and 4 described above.

Finally the invention also relates to the use of the ordered mesoporousor mesostructured compound according to the invention and of the productobtained by the process according to the invention as a catalyst orcatalyst support in particular for automobile post-combustion.

The following examples illustrate the invention without however limitingits scope.

EXAMPLES Example 1 Preparation of a Compound of Cerium Nanoparticles ina Matrix of Alumina Al₂—O₃ With an (Al/Ce) Ratio=(0.1/0.9) Mole et φ=0.2

1-a) Preparation of an Aqueous Colloidal Dispersion of CrystallizedCerium Oxide Particles of Nanometric Dimensions:

A colloidal dispersion of cerium oxide is prepared following theprocedure described in Example 1 of patent application EP 208 580. Thecerium hydrate content is 65% by mass. 300 g of demineralized water isadded to 500 g of redispersable cerium hydrate. An Ultraturax dispersionis then carried out for 15 minutes at 4500 rpm. The dispersion iscentrifuged for 15 minutes at 4500 rpm. A moist pellet is recovered. 200g of demineralized water is added to this moist pellet, the total volumeof the dispersion after addition of water being 300 ml. After Ultraturaxhomogenization for 15 minutes, the dispersion is centrifuged for 45minutes at 4500 rpm. A pellet is recovered. Demineralized water is againadded to this moist pellet up to a total volume of 600 ml. Afterhomogenization, a colloidal dispersion clear to the eye is obtained thatis concentrated by ultrafiltration to 330 ml. This is taken up indemineralized water up to a volume of 600 ml. This is concentrated to200 ml.

After determination of the loss by combustion of the dispersion ofdensity 1.92, the molar concentration of Ce0₂ is 5.69 M or 2.95 mol/kg.

The functionalization of the surface of the CeO₂ nanoparticles iscarried out as follows:

A solution prepared by adding 30.92 g of aminohexanoic acid into 400 mlof water is added to 400 g of colloidal dispersion prepared as describedpreviously. This is left under stirring at ambient temperature for 16hours. The pH is 4.6. The dispersion is again washed by ultrafiltrationby adding two equivalent volumes of demineralized water. This isconcentrated to 500 ml. The dispersion thus obtained is 2.08 mol/l.

After dilution with 1 M/l demineralized water, the pH of the dispersionis 4.3 and the conductivity of the dispersion is 3.15 mS/cm.

1-b) Preparation of an Aqueous Colloidal Dispersion of Particles ofAluminium Trihydroxide (Al (OH)₃) of Nanometric Dimensions:

A colloidal dispersion of aluminium trihydroxide is prepared accordingto the procedure described below:

In a double-envelope reactor equipped with a stirring system and acondenser, 121 g of aluminium salt AlCl₃, 6H₂O are added to 150 g ofwater under stirring,. After dissolution, 154 ml of 3.25 M NH₄OH isadded at 5 ml/minute at ambient temperature. Then 45 g of ureapreviously dissolved in 50 g of water is added.

The reaction medium is maintained at 95° C. for 16 hours.

After cooling to ambient temperature, the pH is pH 6.09.

The dispersion is transferred into a beaker equipped with a pH electrodeconnected to a pH adjustment device. Hydrochloric acid is added understirring over an hour in order to adjust the pH of the dispersion to pH4. This is left under stirring for another hour.

The dispersion is washed with 4 times its volume of demineralized waterby ultrafiltration on 3 KD membranes.

The dispersion is concentrated by ultrafiltration and determination ofthe dry extract by calcination of an aliquot at 1000° C. indicates aconcentration of 1.1 mole in Al.

The concentration of the 1 M dispersion in Al is adjusted by dilutionwith demineralized water.

The pH is equal to 4.65 and the conductivity is 4.5 mS/cm. Usingtransmission electron cryomicroscopy, fully individualized nanoparticleswith a diameter of 3 nm are viewed.

1-c) Preparation of the Mesostructured Material:

200 g of water, then 6.10 g of Pluronic P 123 are poured into a beaker.This Pluronic P 123 compound is an amphiphilic copolymer of tri-blockblock type from the company BASF having as structural formulaHO(CH₂CH₂0)₂₀(CH₂CH (CH₃)O)₇₀(CH₂CH₂0)₂₀H and an average molecular massof 5750 g/mole. The mixture produced was thus subjected to stirring fortwo hours. There followed the simultaneous addition of 56.3 ml of the 1M cerium oxide colloidal dispersion previously described and 6.3 ml ofthe 1 M aluminium trihydroxide colloidal dispersion previouslydescribed. The stirring was continued for 15 minutes.

The dispersion obtained was then placed in glass Petri dishes andsubjected to evaporation at 20° C. for 5 days under a fume hood.

The dry product was then transferred into alumina combustion boats. Theproduct was calcined at 500° C. with a temperature rise of 1° C./minuteand a stage of 6 hours.

The quantities of amphiphilic copolymer and colloidal dispersion thusused verify the φ ratio=0.2.

Transmission electron microscopy observation of the material obtained atthe end of these different stages shows the existence of a texture.

Moreover, the line of the nitrogen BET adsorption-desorption curves showa monodisperse pore-size distribution.

The specific surface area of the material was determined as being equalto 200 m²/g for the product calcined at 400° C. for 6 hours, i.e. 1360m²/cm³.

The specific surface area of the material was determined as being equalto 158 m²/g for the product calcined at 500° C. for 6 hours, i.e. 1075m²/cm³.

The specific surface area of the material was determined as being equalto 110 m²/g for the product calcined at 600° C. for 6 hours i.e.748m²/cm³.

Moreover, the average pore size for these different products wasdetermined as being equal to 7 nm.

The pore volume determined by nitrogen BET is ν_(p)=0.33 cm³/g. UsingX-ray diffraction, streaks characteristic of the Ce0₂ structure wereobserved.

Example 2 Preparation of a Compound of Cerium Nanoparticles in a Matrixof Alumina Al₂O₃—CeO₂ with an (Al/Ce) Ratio=(0.25/0.75) Mole and φ=22

200 g of water, then 6.10 g of Pluronic P 123 were poured into a beaker.The mixture produced was thus subjected to stirring for two hours. Therefollowed the simultaneous addition of 52.2 of the 1 M cerium oxidecolloidal dispersion previously described and 17.4 ml of the 1 Maluminium trihydroxide colloidal dispersion previously described. Thestirring was continued for 15 minutes.

The dispersion obtained was then placed in glass Petri dishes andsubjected to evaporation at 20° C. for 4 days under a fume hood.

The dry product was then transferred into alumina combustion boats. Theproduct was calcined at 500° C. with a temperature rise of 1° C./minuteand a stage of 6 hours.

The quantities of amphiphilic copolymer and colloidal dispersion thusused verify the φ ratio=0.22.

Transmission electron microscopy observation of the material obtained atthe end of these different stages shows the existence of a texture.

The specific surface area of the material was determined as being equalto 127 m²/g at 500° C. i.e. 784 m²/cm³.

Moreover, the average pore size was determined as being equal to 9 nm.

The pore volume determined by nitrogen BET is ν_(p)=0.325 cm³/g.

Example 3 Preparation of a Zirconium-doped Mesostructured Material:Zr-doped Al(OH)3—CeO₂

A 1.2 M solution of Zr(NO₃)₃ in Zr is prepared by adding demineralizedwater to 54.8 ml of 2.19 M solution of Zr(NO₃)₃ in Zr, of density 1.368and 270 g/l zirconium oxide content, until a final volume of 100°cm³ isobtained. 12 g of the mesoporous product, obtained in Example 1-c)above, Al(OH)₃—Ce0₂(((Al:Ce)_(mole)=(0.1:0.9) i.e. 66 millimoles of Ceand 7.2 millimoles of Al), calcined at 400° C. for 6 hours with 8.16 cm³of solution is impregnated with the 1.2 M solution of zirconium nitratein Zr previously prepared (i.e. 9.8 millimoles of Zr). The molar ratio(Zr/Ce) is then equal to 0.15. The product is dried at ambienttemperature for 16 hours, then at 80° C. for 8 hours. The product isthen calcined under air atmosphere at 400° C. with a temperature rise of1° C./minute and a stage of 6 hours.

The impregnation and heat treatment operation is then repeated. Thefinal molar ratio (Zr/Ce) is then equal to 0.3.

Using X-ray diffraction, a spectrum of the particle is observed which isvery close to that of pure cerium oxide, with peaks shifted veryslightly towards small distances (mesh parameters of 5.40 A°) and thepresence of quadratic ZrO2 in very small proportions.

By plotting the adsorption-desorption isotherms, the specific surfacearea is determined as being equal to 125 m²/g.

A pore distribution centred on a pore diameter of 8 nm is observed.

The pore volume is determined as being equal to 0.26 cm³/g.

According to the TPR test, a reducibility peak is observed at a very lowtemperature centred on a temperature of 350° C. The integratedreducibility percentage up to 700° C. is 64%.

Example 4 Preparation of a Praseodymium-Doped Mesostructured Material:Pr-doped Al (OH)₃—CeO₂

A 1.21 M solution of Pr(NO₃)₃ in Pr is prepared by adding demineralizedwater to 51.9 ml of 2.91 M solution of Pr(NO₃)₃ in Pr, of density of1.73 and 28.6% praseodymium oxide content, from the company RhodiaTerres Rares, until a final volume of 125 cm³ is obtained.

10 g of the mesoporous product, obtained in Example 1-c) above,Al(OH)₃—Ce0₂(((Al:Ce)_(mole)=(0.1:0.9) i.e. 55 millimoles of Ce, and 6millimoles of Al), calcined at 400° C. for 6 hours with 6.8 cm³ ofsolution is impregnated with the 1.21 M solution of praseodymium nitratein Pr previously prepared (i.e. 8.23 millimoles of Pr). The molar ratio(Pr/Ce) is then equal to 0.15. The product is dried at ambienttemperature for 16 hours, then at 80° C. for 8 hours. The product isthen calcined under air atmosphere at 400° C. with a temperature rise of1° C./minute and a stage of 6 hours.

The impregnation and heat treatment operation is then repeated. Thefinal molar ratio (Pr/Ce) is then equal to 0.3.

Using X-ray diffraction, a spectrum of the particle is observed which isvery close to that of pure cerium oxide, with peaks shifted veryslightly towards large distances (mesh parameters of 5.45 A°).

By plotting the adsorption-desorption isotherms, the specific surfacearea is determined as being equal to 112 m²/g.

A pore distribution centred on a pore diameter of 7 nm is observed. Thepore volume is determined as being equal to 0.0.29 cm³/g.

Example 5 Preparation of a Titanium-Doped Mesostructured Material:Ti-doped Al (OH)₃—CeO₂

An acidified solution of butyl titanate is prepared by dissolving 20.65g of 23.45% Ti(OBu)₄ in TiO₂ in 15 cm³ of ethanol, and 8 cm³ of 15 MHNO₃ which are made up to 50 cm³ with ethanol.

4 g of the mesoporous product, obtained in Example 1-c) above,Al(OH)₃—Ce0₂(((Al:Ce)_(mole)=(0.1:0.9) i.e. 22 millimoles of Ce),calcined at 400° C. for 6 hours with 2.72 cm³ of solution is impregnatedwith the titanium solution previously prepared (i.e. 3.26 millimoles ofPr). The molar ratio (Pr/Ce) is then equal to 0.15. The product is driedat ambient temperature for 16 hours, then at 80° C. for 8 hours. Theproduct is then calcined under air atmosphere at 400° C. with atemperature rise of 1° C./minute and a stage of 6 hours.

Using X-ray diffraction, a spectrum of the particle is observed which isvery close to that of pure cerium oxide, with peaks shifted veryslightly towards small distances.

By plotting the adsorption-desorption isotherms, the specific surfacearea is determined as being equal to 165 m²/g.

A pore distribution centred on a pore diameter of 7 nm is observed.

The pore volume is determined as being equal to 0.32 cm³/g.

Example 6 Preparation of Mesostructured Material Ce-Doped Al(OH)₃—ZrO₂

6-a) Preparation of the Dispersion of Al(OH)₃:

A colloidal dispersion of Al(OH)₃ prepared following the proceduredescribed in Example 1-a) except that dilution is to 0.57 mol/kg.

The characteristics of the colloidal dispersion obtained are:

-   -   Concentration 0.57 mole/kg in Al    -   Conductivity=11.2 mS/cm    -   pH=4.7        6-b) Preparation of the Colloidal Dispersion of ZrO₂ Modified by        Caproic Acid:

A colloidal dispersion of ZrO₂, from Nyacol, containing 20% by weightZr0₂, density 1.32, at 2.15 mol/l is ultrafiltrated on a 3KD membrane.After washing with 6 volumes of water, the colloidal dispersion has thefollowing characteristics: pH 1.84, conductivity 17 mS/cm, concentration1.46 mol/l Zr0₂. The colloids possess a diameter of approximately 3 nm.

100° cm³ of colloidal dispersion of colloids of ZrO₂ modified with a 1 Mcaproic amine are prepared by mixing:

-   -   68.49 cm³ of 1.46 M dispersion (i.e. 100 millimoles of Zr),    -   31.51 cm³ of a solution containing 3.935 g of aminocaproic acid        (i.e. 30 millimoles of caproic acid, MW=131 g).

This is left under stirring for 30 minutes and allowed to rest for 16hours at ambient temperature.

The dispersion is ultrafiltrated on a 3 KD membrane by 2 equivalentvolumes of water.

The characteristics of the colloidal dispersion are: pH 4.28, s=10.25mS/cm and 0.8 mol/kg in Zr.

6-c) Preparation of the Mesostructured Material Al(OH)₃—Zr0₂(Al:Zr)=(0.1:0.9) Mole by Self-Assembly of the Nanoparticles:

The following are mixed at ambient temperature:

-   -   55.15 g of the colloidal dispersion of ZrO₂ modified with        aminocaproic acid at 0.8 mol/kg (containing 45 millimoles of Zr)    -   8.596 g of Al(OH)₃ sol at 0.57 mole of Al/kg (containing 5        millimoles of Al)    -   81.6 cm³ of a 50 g/l POE PPO POE (P123) solution (containing        4.08 g of P123).

This is left under stirring for 30 minutes.

The mixed dispersion is poured into thin-film crystallizing dishesapproximately 1 cm thick. It is then left to evaporate at ambienttemperature for 4 days. The solid product is calcined at 400° C. Thetemperature rise is 1° C./minute and the 400° C. stage lasts 6 hours.

The product obtained possesses a vermicular-type structure, shown bytransmission electron microscopy.

The specific surface area is 186 m²/g. BET analysis shows a monodispersepore distribution centred on 6 nm and a pore volume of the order of 0.22cm³/g. Using X-ray diffraction, streaks are observed showing acommencement of ZrO₂ crystallisation corresponding to the tetragonalstructure.

6-d) Doping of the Mesostructured Product Obtained in Example 6-c) withCerium (Ce)

A 0.64 M Ce⁴⁺ impregnation solution is prepared by dilution withdemineralized water to a final volume of 200 cc of an aliquot of 68.8cm³ of ceric nitrate solution, (Rhodia La Rochelle, characteristicsCe(NO₃)₄, (H+/Ce) mole=0.5 and 1.86 M Ce⁴⁺).

118.5 g of mesostructured product (0.9 ZrO₂-0.1 Al(OH)₃) contain 0.9mole of Zr0₂ and 0.1 mole of Al(OH)₃. 1 g of mesostructured product (0.9ZrO₂-0.1 Al (OH)₃) contains 7.6 millimoles of Zr and 0.84 millimole ofAl.

The impregnation is carried out with 0.59 cm³ of Ce(N0₃)₄ solution (i.e.0.38 millimole of Ce⁴⁺) previously described per gram of nanostructuredproduct. This impregnation is carried out by kneading the paste atambient temperature. The Ce/Zr molar ratio=0.05.

The reaction medium is left to dry at ambient temperature for 16 hoursthen calcined at 400° C. for 6 hours. The temperature rise is 1°C./minute.

The impregnation, drying and calcination operations are repeated threetimes. The Ce/Zr molar ratio=0.2.

Using X-ray diffraction, a Zrl_(1-x)Ce_(x)O₂ structure and a minorityquantity of Ce0₂ are shown.

6-e) “TPR” Evaluation

Using the “TPR” protocol described above, two reducibility peaks areobserved, corresponding to maximum temperatures of approximately 375° C.(majority peak) and a second (minority) peak towards 550° C. It will berecalled that the cerium-doped ZrO₂ materials develop a reducibilitypeak observed at 550° C.

A reducibility percentage between 200° C. and 650° C. of 80%, large incomparison to the reducibility percentages normally found, is determinedfor the cerium-doped ZrO₂ products.

1-34. (canceled)
 35. An ordered mesoporous or mesostructured compoundcomprising a mineral phase of alumina, within which at least partiallycrystalline particles of a cerium, titanium or zirconium compound aredispersed, and having a chemical homogeneity such that the heterogeneitydomains are at most 100 nm².
 36. The compound according to claim 35,having a chemical homogeneity such that the heterogeneity domains are atmost 25 nm².
 37. The compound according to claim 35, further having anoverall degree of crystallinity by volume of at least 10%.
 38. Thecompound according to claim 37, wherein the overall degree ofcrystallinity by volume is of at least 30%.
 39. The compound accordingto claim 35, wherein the particles are particles of cerium and whereinthe alumina and the cerium are present in a quantity providing an atomicratio Ar=Al/(Ce+Al) of at most 50%, optionally at most 25%.
 40. Thecompound according to claim 35, having walls whose overall thickness iscomprised between 2 and 10 nm.
 41. The compound according to claim 35,wherein the particles dispersed in the mineral phase present a diameterof 3 nm to 5 nm.
 42. The compound according to claim 35 having poreswith a size comprised between 2 and 12 nm.
 43. The compound according toclaim 35, having at least locally a mesostructure selected from thegroup consisting of mesoporous mesostructure of P63/mmcthree-dimensional hexagonal symmetry, P6mm two-dimensional hexagonalsymmetry, Ia3d, Im3m or Pn3m three-dimensional cubic symmetry;vesicularmesostructure; lamellar mesostructure; or vermicularmesostructure.
 44. The compound according to claim 35, wherein theparticles include at least one element M in solid solution in saidparticles.
 45. The compound according to claim 44, wherein said elementM is selected from the rare earths and the transition metals, and iscapable of being integrated in cationic form in solid solution withinsaid particles.
 46. The compound according to claim 45, wherein saidelement M is cerium, titanium, zirconium, manganese, lanthanum,praseodymium or neodymium, with the proviso that said element M isdifferent from the element cerium, titanium or zirconium constitutingsaid particle.
 47. The compound according to claim 46, comprisingparticles of a cerium compound and wherein the element M is a rare earthor zirconium, with a molar ratio M/Ce of at most
 1. 48. The compoundaccording to claim 46, comprising particles of a cerium compound andwherein the element M is titanium with a molar ratio Ti/Ce of at most0.5.
 49. The compound according to claim 35, wherein said particlesfurther comprise at least one element M′ at least in part on theirsurface.
 50. The compound according to claim 49, wherein the element M′is manganese, an alkali metal or an alkaline earth metal.
 51. A processfor the preparation of an ordered mesoporous or mesostructured compoundcomprising a mineral phase of alumina, within which at least partiallycrystalline particles of a cerium, titanium or zirconium compound aredispersed, and having a chemical homogeneity such that the heterogeneitydomains are at most 100 nm², said process comprising the steps of: 1)forming an aqueous mixture comprising a colloidal dispersion of alumina;at least one texturing agent; a colloidal dispersion of a cerium,titanium or zirconium compound in which the cerium, titanium orzirconium compound is functionalized by a surfactant of formula:X-A-Y wherein: X is a function that complexes the cation of the cerium,titanium or zirconium compound of the colloidal dispersion; A is alinear or branched alkyl-type group; and Y is an amine or hydroxy group;the colloidal dispersions of alumina and of the cerium, titanium orzirconium compound having a conductivity below 25 mS/cm; 2) eliminatingthe water from the mixture formed in step 1); 3) eliminating thetexturing agent; and 4) recovering the mesoporous or mesostructuredcompound.
 52. The process according to claim 51, wherein the colloidaldispersion of alumina has a pH of between 3 and
 6. 53. The processaccording to claim 52, wherein the colloidal dispersion of alumina has asize of colloids of between 1 and 5 nm.
 54. The process according toclaim 51, wherein the texturing agent is a non-ionic copolymersurfactant.
 55. The process according to claim 54, wherein the copolymeris a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)triblock copolymer, a poly(ethylene oxide)-poly(isopropene) blockcopolymer or a poly(ethylene oxide)-poly(isoprene) block copolymer. 56.The process according to claim 51, wherein the colloidal dispersion of acerium, titanium or zirconium compound is a colloidal dispersion of acerium, titanium or zirconium oxide and the surfactant are present witha Rb ratio (Rb=number of moles of function X/number of moles of cerium,titanium or zirconium oxide), of between 0.1 and 0.5.
 57. The processaccording to 51, wherein the colloidal dispersion of a cerium,. titaniumor zirconium compound present colloids whose average size is between 3and 8 nm.
 58. The process according to one of claim 51, wherein thesurfactant is an amino acid, optionally an aliphatic amino acid.
 59. Theprocess according to claim 51 wherein, in step 1), the mixture has aconductivity, measured at a concentration of 1 M, of at most 25 mS/cm.60. The process according to claim 59, wherein the conductivity is atmost 8 mS/cm.
 61. The process according to one of claims 17 to 26wherein the colloidal dispersions and the texturing agent are inquantities such that the ratio Φ (Φ=volume of the colloids/volume of thecolloids+volume of the texturing agent) is between 0.1 and 0.6,optionally between 0.1 and 0.4.
 62. The process according to claim 51,wherein in step 2), the water is eliminated from the mixture formed instep 1), by evaporation or by spray-drying.
 63. The process according toclaim 51, wherein in step 3), the texturing agent is eliminated by aheat treatment.
 64. The process according to claim 51, wherein in step1), the functionalization of the cerium, titanium or zirconium compoundis carried out by adding a colloidal dispersion of said compound to thesurfactant.
 65. A process for the preparation of an ordered mesoporousor mesostructured compound comprising a mineral phase of alumina, withinwhich at least partially crystalline particles of a cerium, titanium orzirconium compound are dispersed, and having a chemical homogeneity suchthat the heterogeneity domains are at most 100 nm², said particlesincluding at least one element M in solid solution in said particles,said element M being selected from the rare earths and the transitionmetals, and being capable of being integrated in cationic form in solidsolution within said particles, said process comprising the steps of: 1)forming an aqueous mixture comprising a colloidal dispersion of alumina;at least one texturing agent; a colloidal dispersion of a cerium,titanium or zirconium compound in which the cerium, titanium orzirconium compound is functionalized by a surfactant of formula:X-A-Y wherein: X is a function that complexes the cation of the cerium,titanium or zirconium compound of the colloidal dispersion; A is alinear or branched alkyl-type group; and Y is an amine or hydroxy group;the colloidal dispersions of alumina and of the cerium, titanium orzirconium compound having a conductivity below 25 mS/cm; 2) eliminatingthe water from the mixture formed in step 1); 3) eliminating thetexturing agent; and 4) recovering said compound by: 4-a) adding themixture obtained at the end) of step 3), to a solution of an element Mselected from the rare earths and the transition metals, being capableof being integrated in cationic form in solid solution within saidparticles and having a concentration of this element of at most 2 mol/l;4-b) calcining the mixture obtained at the end of step 4-a) at atemperature of at most 500° C.; and, optionally, 4-(c) repeating steps4-a) and 4-b) until obtaining the compound with a desired level ofelement M.
 66. The process according to claim 65, wherein the step 4-a)is done by dry impregnation.
 67. A process for the preparation of anordered mesoporous or mesostructured compound comprising a mineral phaseof alumina, within which at least partially crystalline particles of acerium, titanium or zirconium compound are dispersed, and having achemical homogeneity such that the heterogeneity domains are at most 100nm², said particles comprising at least one element M′ at least in parton their surface, said element M′ being manganese, an alkali metal or analkaline earth metal, said process comprising the steps of: 1) formingan aqueous mixture comprising a colloidal dispersion of alumina; atleast one texturing agent; a colloidal dispersion of a cerium, titaniumor zirconium compound in which the cerium, titanium or zirconiumcompound is functionalized by a surfactant of formula:X-A-Y wherein: X is a function that complexes the cation of the cerium,titanium or zirconium compound of the colloidal dispersion; A is alinear or branched alkyl-type group; and Y is an amine or hydroxy group;the colloidal dispersions of alumina and of the cerium, titanium orzirconium compound having a conductivity below 25 mS/cm; 2) eliminatingthe water from the mixture formed in step 1); 3) eliminating thetexturing agent; and 4) recovering said compound by: 4-a′) the materialobtained previously is brought into contact with a solution of theelement M′ which has a concentration of this element of at least 1.5mol/l; 4-b′) the material obtained after this bringing into contact withsaid solution is calcined at a temperature of at most 500° C.; and,optionally, 4-c′) repeating seps 4-a′) and 4-b′) until obtaining thecompound with a desired level of element M′.
 68. A catalyst support inparticular for automobile post-combustion, comprising a compound asdefined in claim 35.